Full Body Workout vs. Focused Muscle Group

So most of my time in the gym my programs normally are full-body workouts. I'm getting bored with those to be honest, and I'm not seeing the results that I'd like.

I'm trying to get leaner, but I don't know if it's the program or just me. I wanted to give a focused muscle group program a chance, but I'm not sure if they're any good as I've always heard negative opinions of them.

Can you guys with more experience please offer some guidance and advice on which is better for results and the pros/cons of each? Thank you so much!